I can point to :
1. The North Sea coast route following bike paths along the coast until Boulogne sur Mer (route 6 on the map) and then dropping to Paris.
2. A variant on this that leaves the coast by going over Gent (Ghent) or Brugge (Brueghes) to Ieper (Ypres) and dropping to Paris
3. The so-called Van Gogh route passing over Antwerpen, Brussel(s) - route 1 on the map
4. A variant over Eindhoven (where I live), joining the Van Gogh route in Brussels
5. A route passing over Eindhoven and Maastricht and joining a route coming from Aachen (Aken in dutch) - route 7 on the map
Depending on what you want to see and taste (cities, art, history, beers, quiet roads?), you should select one of these. I could probably assist you in finding guides including maps and stages and lodging information, probably in dutch but probably not difficult to decipher.
I don't believe there is urgency in booking rooms, possibly excepting Paris and Amsterdam. If your ride is in July, booking in May seems quite timely.